Moment actuated transducer

ABSTRACT

A moment-actuated transducer unit mounted to an elastic belt having Velcro-type fastener means for attaching the belt and transducer unit snugly around the chest or abdomen region of a subject&#39;&#39;s body provides a highly sensitive and easily installed respiration transducer assembly. The output of the transducer unit can be connected directly to a high input impedance recorder or to a signal conditioning circuit which includes an unfiltered output and a high frequency filtered output wherein a regular high input impedance recorder can be selectively connected to either of such outputs.

United States Patent [191. R eibold MOMENT ACTUATED TRANSDUCER [76]Inventor: Robert C. Reibold, 12062 Brookhaven Pk., Garden Grove, Calif.92640 [22] Filed: Dec. 8, 1972 [21] Appl. No.: 313,537

Related US. Application Data [62] Division of Ser. No. 146,156, May 24,1971.

[52] US. Cl 310/85, 310/86, 310/91 [51] Int. Cl l-l04r 17/00 [58] Fieldof Search 310/82, 8.3, 8.5,

[56] References Cited UNITED STATES PATENTS 3,546,497 12/1970 Craster3l0/8.5 X 3,564,402 2/1971 Pittman 3/1966 Burkhalter et al 3l0/8.6

[ Jan. 15, 1974 Primary Examiner-Gerald Goldberg Assistant Examiner-MarkO. Budd Attorney- D. N. .leu, Walter .1. Jason and Donald L.

Royer [57] ABSTRACT A moment-actuated transducer unit mounted to anelastic belt having Velcro-type fastener means for attaching the beltand transducer unit snugly around the chest or abdomen region of asubjects body provides a highly sensitive and easily installedrespiration transducer assembly. The output of the transducer unit canbe connected directly to a high input impedance recorder or to a signalconditioning circuit which includes an unfiltered output and a highfrequency filtered output wherein a regular high input impedancerecorder can be selectively connected to either of such outputs.

3 Claims, 12 Drawing Figures Geil et al. 310/85 X PATENTEU 3.786285SHEET 1 0F 2 [143/75 JAY/17 i "MOMENTACTUATED TRANSDUCER This is adivision of application Set. No. l46,l56 filed May24, 1971.

BACKGROUND OF THE INVENTION My present invention relates generally tophysiological measuring apparatus and, more particularly, to a means forobtaining accurate respiration data from human or other animal subjectseither at rest or during intense activity thereof with negligibleinterference of their normal functions.

In the measurement'of respiration data, a thermistor face mask whichencloses the nose and mouth areas of the subject is commonly used tomeasure the confined air temperature and its variation in order todetermine respiration rate and volume. The thermistor mask is, however,encumbering to the wearer and relatively complex conditioning of thethermistor output signal is required to provide a useful signal whichcan be applied directly to an ordinary recorder. Of course, a face maskcannot be used on animals without greatly interfering withtheir normalactivities.

Strain gage type transducers for sensing, stress changesdueto expansionorcontraction of the skin area to whichthey are affixedhave beenemployed to avoid the use of face masks. Such transducers are, however,cumbersome becauseof their (beam) size and they must normally be used ina bridge circuit. Further, the strain type transducer is relativelyinsensitive and also requires relatively complex signal conditioningbefore its output signal can be usefully applied to a regular recorder.L

An impedance pneumograph can be utilized to avoid the use of face masks.The pneumograph essentially measures the movements of the chest wallduring respiration as changes in impedance between attached chestelectrodes. It is, however, more troublesome to use because of therequirement for good electrical contacts with ,a subjects body. As inthe preceding devices, it also requires relatively complex signalconditioning of its output 'signal'before it can be feasibly applied toan ordinary recorder.

SUMMARY or THE INVENTION Briefly, and in general terms, my invention ispreferably accomplished by providing a highly sensitive and easilyinstalled respiration transducer assembly including a moment-actuatedtransducer unit. mounted to an elastic belt having Velcro-type fastenermeans for attaching the belt and transducer unit snugly around the chestor abdomen portion of a subject's body, the output of the transducerunit being connectable directly to a high input impedance recorder orindirectly to a low input impedance recorder through a signalconditioning circuit (wherein such recorder is connected to theunfiltered output thereof).

'The transducer unit comprises a piezoelectric element including a thinpiezoelectric crystal cemented to the front face of a thin metallic(beam) disc, a pair of parallel attachment (bending arm) loops affixedrigidly to the rear face of the metallic disc and protrudingperpendicularly a predetermined distance before the front face thereof,a pair of electrical leads soldered respectively to the piezoelectriccrystal and metallic disc, and a layer of resilient materialencapsulating the piezoelectric element and inner portions of theattachment loops and electrical leads adjacent to the piezoelectricelement. The elastic belt is connected to the exposed portions of theattachment loops and is used to support the transducer unit.

The signal conditioning circuit comprises an attenuator having anunfiltered output and a filtered output including a low pass filterhaving a cut-off frequency of about 0.2 hertz to reject higher frequencysignals than the respiration signals, such as those caused by motion orvibration of the transducer unit when the subject is running. Theconditioning circuit presents a high input impedance to the transducerunit and a low output impedance to a recorder or the low pass filter. Ahigh or low input impedance recorder can be connected to the unfilteredoutput; however, a sufficiently high input impedance recorder which doesnot load the low pass filter should ordinarily be connected to thefiltered output. The capacitance of the transducer unit and the shuntinginput impedance (resistance) of the conditioning circuit provides arelatively long time constant which permits the system to beself-balancing.

BRIEF DESCRIPTION OF THE DRAWINGS My invention will be more fullyunderstood, and other features and advantages thereof will becomeapparent, from the description given below ofan exemplary embodiment ofthe invention. This description of the exemplary embodimentof theinvention is to be taken in conjunction with the accompanying drawings,in which:

FIG. 1 is a top plan view of a transducer assembly constructed inaccordance with this invention and shown in' positionto be fastenedabout the lower chest or diaphragm area of a persons body;

FIG. 2 is a front elevational view of a piezoelectric element used inthe construction of a transducer unit which is a component of thetransducer assembly shown in FIG. 1; j t

FIG. 3 is a top plan view of the piezoelectric element shown in FIG. 2;

FIG. 4 is a side elevational view of an attachment loop used in theconstruction of the transducer unit component;

FIG. 5 is a top plan view of the attachment loop shown in FIG. 4;

FIG. 6 is a front elevational view of the transducer unit componentprior to encapsulation thereof;

FIG. 7 is a top plan view of the unencapsulated transducer unitcomponent shown in FIG. 6;

FIG. 8 is a front elevational view of the transducer unit component usedin the transducer assembly of FIG. 1;

FIG. 9 is a top plan view of the transducer unit component shown in FIG.8;

FIG. I0 is a circuit diagram of a signal conditioning circuit which ispreferably used with the transducer assembly of FIG. 1;

FIG. 11 is a graph showing a curve of a respiration signal recorded by arecorder connected to the unfiltered output of the signal conditioningcircuit of FIG. 10; and I FIG. 12 is another graph showing a curve of arespiration signal recorded by the recorder when connected to thefiltered output of the signal conditioning circuit of FIG. 10.-

former coupling occurring when the toroidal magnetic core 17 is in anunsaturated condition. The amplitude of the signal that is transformercoupled to the same wire 21 is dependent upon the distance the magnet 18is relative to the toroidal magnetic core 17.

Time delay means 22 is connected between the oscillating voltage source12 and the switching circuit 13 to substantially parallel the signalpath, passing through the toroidal magnetic core 17. The time delaymeans 22 preferably comprises a trigger circuit 23 and a seriesconnected time delay circuit 24. The trigger circuit 23 may be a Schmitttrigger device, or may be any other suitable trigger device having aminimum threshold input level.

In operation, the oscillator drives the amplifier to such an extent toprovide a sufficient output voltage across the primary winding formed bythe drive line 19. This voltage is induced into the secondary windingformed by the sense line 21 when the toroidal magnetic core 17 is in anunsaturated condition. When the core is saturated the voltage decreasesto zero and no output signal will be obtained.

The output of the oscillator circuit 12 also feeds the trigger circuitwhich produces a square wave output signal in phase with the sine wave.This is delivered to the delay circuit 24 to delay the positive pulsessufficient so that the positive edge occurs when voltage at the input ofthe flip-flop 14 is at its maximum. It will be understood that the delayfunction also can be accomplished by changing the trigger level of thetrigger circuit 23.

The induced positive voltage in the secondary winding formed by thesense line 21 is sampled at the input terminal 14 of the flip-flop onpositive edge of the clock. If the positive voltage is of sufficientmagnitude the flip-flop will change to a logic one state and provide afeedback signal through a resistor 26. This feedback signal provides abounceless output and an electrical hysteresis characteristic for thecircuit. In the illustrated embodiment the signal delivered across thesense line 21 passes through a series resistor 27.

Referring now to FIG. 2 there is seen an alternate form of the solidstate switch control circuit constructed in accordance with theprinciples of this inventionand is designated generally by referencenumeral 30. Here a pulsating voltage source 31 is formed by a clockgenerator and is used to control the operation of a switching circuit32. The switching circuit 32 is again shown as a flip-flop circuitsimilar to that disclosed with regard to FIG. 1. By utilizing the clockgenerator 31 the oscillator and Schmitt trigger configuration of FIG. 1can be eliminated. The switching circuit 32 includes an input terminal33 and a clock input terminal 34 which functions substantially in thesame manner as disclosed above.

A toroidal magnetic core 36 is capable of being magnetically saturatedand unsaturated as a result of movement of an associated permanentmagnet 37. A drive wire 38 passes'through the toroidal magnetic core andhas one end thereof coupled to an amplifier 39 and the other end thereofconnected to a terminal point 40 located between a resistor 41 and acapacitor 42. A sense wire 43 also passes through the toroidal magneticcore and functions as the secondary winding of a transformer when thecore is in the magnetically unsaturated condition. A delay line circuitpath is provided by a delay circuit 46 which parallels the signal pathprovided through the toroidal magnetic core.

The flip-flop circuit 32 is provided with a feedback resistor 47 whichfunctions in the same manner as the resistor 26 of FIG. 1. The amplifier39 and time delay circuit 46 operate in synchronization with one anotherto provide input signals to the switching input terminal 33 and theclock input terminal 34. When the signal level at terminal 33 is ofsufficient amplitude the flipflop will switch to its high state and whenthe signal level drops below a given level the flip-flop willautomatically switch back to its low state.

For-a better understanding of the circuit of FIG. 2 reference is nowmade to FIG. 3 which is a more detailed showing of the circuitconfiguration. Here the clock circuit is illustrated by referencenumeral 50 and comprises three invertor circuits 51, 52, and 53connected in series with a capacitor 54 connected across the invertor52. The time delay circuit is designated generally by reference numeral55 and comprises a pair of series connected invertor circuits 56 and 57.The amplifier comprises a single transistor 58 and a resistor 59 havingthe emitter thereof connected to ground potential and collector thereofconnected to the circuit point 40. The drive wire 38 is connected to thecircuit point 40 and provides a current coupling output pulse whentransistor 58 is rendered conductive to discharge capacitor 42.

While several specific embodiments are illustrated herein it will beunderstood that still other circuit configurations can be utilizedwithout departing from the spirit and scope of the novel conceptsdisclosed and claimed herein.

The invention is claimed as follows:

1. A solid state switch control circuit, comprising in combination: anoscillating voltage source, a switching circuit having a switching inputterminal, said switching circuit capable of being activated to aswitched state when an input signal at said switching input terminal isabove a predetermined voltage level, a closed magnetic core structurecapable of being magnetically saturated and unsaturated in response tothe application of a magnetic field, magnet means positioned adjacentsaid closed magnetic core structure for saturating and unsaturating saidcore, a drive wire connected to said oscillating voltage source andpassing it through said closed magnetic core, structure a sense wireconnected to said switching circuit and passing it through said closedmagnetic core structure, said drive and sense wire providing atransformer coupling therebetween when said closed magnetic corestructure is in an unsaturated state, and time delay means connectedbetween said oscillating voltage source and said switching circuit andproviding a parallel signal path to the signal path through said driveand sense wires, whereby actuation of said switching circuit will occuronly when said closed magnetic core structure is sufficientlyunsaturated and when a pulse is applied to said switching circuitthrough said time delay means.

2. The solid state switch control circuit according to claim 1, whereinsaid oscillating voltage source is an oscillator providing a sine wave,and said time delay means includes a trigger circuit connected in serieswith a delay circuit for providing a suitable time delay at a clockinput of said switching circuit.

3. The solid state switch control circuit according to claim 2, furtherincluding amplifier means connected in filter 68 comprises seriesresistor R2 and shunt capacitor C2. The buffer stage 70 includestransistors Q1 and 02 wherein the base of the former transistor isconnected to input terminal 62 by resistor R1 and the emitter isconnected to the base of the latter transistor. The collectors of thetransistors Q1 and Q2 are connected to a source 72 of positive voltage,and the emitter of the latter transistor is connected through seriesconnected resistor R3 and potentiometer R4 to a source 74 of negativevoltage. Series connected resistors R5 and R6 connect the source 72 tothe base of the transistor Q1, and bias it and the transistor O2 to benormally always conducting. The emitter of transistor Q2 is connected tounfiltered output 76 by lead 78, and to filtered output 80 by the R2-C2filter 68, as shown.-Potentiometer or rheostat R4 can be used to adjustthe outputs 76 and 80 to zero or, if desired, to a positive or negativereference base.

In an illustrative and satisfactory embodiment of the signalconditioningcircuit 60, the transistors Q1 and Q2 are each a 2N3391A transistor,resistors R1, R2, R3, R5 and R6 are respectively 100 megohms, S6kilohms, l kilohm, 22 megohms and 22 megohms in value, potentiometer R4is 10 kilohms in resistance, and capacitor C2 is microfarads (mfd.). invalue, for example. The positive and negative voltage sources 72 and 74can be 5-volt batteries; however, where adjustment of the reference baseneed not be to zero, only one 5'-volt battery (72, for example) can beused (R4 connected to ground) and a reference base such as at 2.5 voltscan be utilized.

In operation, the elastic belt 24 (FIG. 1) is fastened snugly (i.e., ata tactually established predetermined tension).around the chest orabdomen portion of a subject, and theelectrical leads 34 and 36 of thetransducer unit 22 are connected to the input terminals 62 and 64ofsignal conditioning circuit 60 (FIG. 10) At least one oftheoutputs 76 or80 is connected to a suitable recorder (not shown). Potentiometer R4 isthen adjusted to produce a zero reference base. Inhalation by thesubject ex'pands theibelt 24 and applies amoment to the. loops 28and 30(bending arms) to cause a further central outward deflection of themetallic disc 58 (brass beam). .This also further deflects thepiezoelectric crystal 56 cemented to the disc 58 and produces a positiveoutput voltage from the outputs 76 and 80. Exhalation, of course,produces the opposite effect and a negative output voltage is producedfrom the outputs 76 and 80 when the deflection of the disc 58 is lessthan its initial, reference base, condition.

The attenuator 66 (FIG. 10) of the signal condition ing circuit 60 alsopresents a high input impedance to the transducer unit 22 and provides alow output impedance which generallymatches the input impedance of a lowinput impedance recorder that can be connected tothe unfiltered output76. Of course, a regular high input impedance recorder can be connectedto either the unfiltered output 76 or the filtered output 80. Asufficiently highinput impedance recorder (which does not load theresistor R2) should, however, be ordinarily connected to the filteredoutput 80.

The capacity (C1 of approximately 0.03 mfd.) of the transducer unit 22shunted by the resistance (approximately 140 megohms) of the resistor R1plus the input impedance of the buffer stage 70 provides a relativelylong R-C time constant of about 5 seconds which. permits the system tobe self-balancing, i.e., when the transducer unit 22 is deflected fromits reference condition, an output voltage is generated therefrom whichreturns to zero by discharging through the resistor R1 and the bufferstage 70. This time constant can, of course, be varied by minormodification of the circuit components. The time constant should not betoo short since the output voltage of the transducer unit 22 then wouldnot follow the higher frequency respiration signal componentsaccurately. On the other hand, an excessively long time constant wouldnot allow any large transient voltage generated by the unit 22 (as froma sharp jolt) to be dissipated or decay with sufficient promptness.

FIG. 11 is a graph showing a curve S which was the respiration signalobtained from the unfiltered output 76 (output voltage v) and producedby a human subject running at approximately 6 m.p.h. on a treadmill. Therespiration rate can be easily determined along the abscissa or timeaxis (time t) but the variation of respiration volume is somewhatobscured or confused by the superimposed, higher frequency, waveletswhich are largely due to the bouncing and vibration of the transducerunit 22 caused by the running motions of the subject. In order toincrease the accuracy and ease of determining both respiration rate andvolume, the filtered output 80 can be used to drive the recorder.

FIG. 12 is a graph, similar to that of FIG. 11, showing a curve y whichwas the respiration signal obtained from the filtered output 80 andproduced by the same running subject. It can be readily seen from anexamination of the curves of S and y that both respiration rate andvolume can be much more accurately and easily determined from the lattercurve. The amplitude of the curve y, as measured from its referencebase, is substantially devoid of the higher frequency and extaneouswavelets so that it clearly yields a far more accurate indication ofinstantaneous respiration volume of the subject. It may be noted thatthe curves of S and y, in FIGS. 11 and 12 are of consecutive signalsproduced by the same running subject, and are not the unfiltered andfiltered forms'of an instantaneously identical signal. i

The respiration measuring system described above has served to obtainrespiration data from human and animal subjects during intense activitythereof or at rest with negligible interference of their normalactivity. The system is unencumbering to the subject and has extremelyhigh sensitivity yet is of simple and inexpensive construction. It isself-balancing and particularly easy to install and operate to providehighly accurate and useful respiration data.

The system is capable of detecting and recording pressure changes ofheart pulses when the transducer unit 22 is located on or near a surfaceartery. In determining pulse pressure and rate, for example, thetransducer assembly 20 can be installed about the forehead of a personwith the transducer unit 22 preferably positioned over a temple regionof the persons head. Where the-transducer assembly 20 is suitablyinstalled about the chest or abdomen of a person, the pulse rate canactually be noted from inspection of the unfiltered but not the filteredrecorded curves of S and y (FIGS. 11 and 12). The pulse pressure signalsappear as small prominences superimposed on the large peaks and valleysof the unfiltered respiration curve S for a person not engaged inintense activity, which activity would produce overriding and obscuringsignals.

While an exemplary embodiment of this invention has been described aboveand shown in the accompanying drawings, it is to be understood that suchembodiment is merely illustrative of, and not restrictive on, the broadinvention and that I do-not desire to be limited in my invention to thedetails of construction or arrangement shown and described, for obviousmodifications may occur to persons skilled in the art.

I claim:

1. In a transducer system of the class described, a transducer unitcomprising:

a disc-like piezoelectric element including a deflectable planar beam,and a piezoelectric crystal bonded to a plane surface of said beam;

a pair of moment arms each including a normally lower and a normallyupper end, said lower ends being affixed in a spaced relationshiptherebetween to said beam with said arms extending angularly apredetermined distance from said surface and intersecting at asubstantial angle of at least about 45 degrees with respect thereto; and

means fastenable to force-generating support means and connecting withsaid arms at least near said upper ends thereof for supporting saidelement and providing a moment on said arms, said connecting meansnormally applying a force from said support means to said arms at leastnear said upper ends thereof in a direction generally parallel to saidsurface to provide said moment which bends said element and produces anoutput signal therefrom.

2. The invention as defined in claim 1 wherein said arms include a pairof loop-like arms each having a normally lower and a normally upper endportion and side portions joining said lower and upper end portionstogether in a closed loop, said lower end portions being affixed in aspaced parallel relationship with respect to each other to said beam andsaid side portions extending angularly a predetermined distance fromsaid surface and intersecting at a substantial angle of at least about60 with respect thereto, said connecting means includes an elastic beltattached at its ends to said upper end portions of said loops, and saidsupport means includes a selected portion of a subject's body, said beltbeing fastened thereabout at a predetermined tension and applying amoment to said arms according to its instantaneous tension whereby saidelement is actuated with expansion and contraction of said belt by saidbody portion to produce a variable output signal from said elementrepresentative of the motions of said body portion.

3. The invention as defined in claim 2 wherein said side portions ofsaid loops extend perpendicularly a predetermined distance from saidsurface, and said belt includes fastener means adjustable to secure saidbelt at a tactually established predetermined tension about said bodyportion.

Pb-wso UNITED STATES PATENT OFFICE Inventofls) v l l 569 CERTIFICATE OFCORRECTION "Patent No. '3 3 5 5 Dated Januar-Y 97 Robert V c. Reibold Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

e I Front; page, left column, Code "[76]" should read --[75]--;- andbelow the Inventor data, insert- [73] Assignee: McDonnell DouglasCorporation, corporation of,1 iary1and--$ line 35, "extaneous" shouldread --'-extraneous-.

, s ned and sealed this 3rd day of December 1974;

(SEAL) f Attest: I v

McCOY GIBSON JR. c. MARS-BALL DANN Attesting Officer Comisexoner ofPatentsmg I UNITED STATES PATENT OFFICES r CERTIFICATE OF CORRECTIONPatent No. 5 f -January l5, 197

Robert C. Reibold Inventor(s) It is certified that error eppears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Front; page, left column, Code "[76]" should read ----[75]---;"[

l and belowthe Inventor data, insert -[73] Assignee: McDonnell DouglasCorporation, a. corDorat-ion of Marylandw-fi 6,

1 line-35, "extaneous" should read -'-extra.neous--.

" Signed and sealed this 3rd day of December 1974.

(SEAL) Attest:

MCCOYMQGIBSON JR. 'c. MARS-IIIALL DANN Attesting Officer Comissloner oifacente

1. In a transducer system of the class described, a transducer unitcomprising: a disc-like piezoelectric element including a deflectableplanar beam, and a piezoelectric crystal bonded to a plane surface ofsaid beam; a pair of moment arms each including a normally lower and anormally upper end, said lower ends being affixed in a spacedrelationship therebetween to said beam with said arms extendingangularly a predetermined distance from said surface and intersecting ata substantial angle of at least about 45 degrees with respect thereto;and means fastenable to force-generating support means and connectingwith said arms at least near said upper ends thereof for supporting saidelement and providing a moment on said arms, said connecting meansnormally applying a force from said support means to said arms at leastnear said upper ends thereof in a direction generally parallel to saidsurface to provide said moment which bends said element and produces anoutput signal therefrom.
 2. The invention as defined in claim 1 whereinsaid arms include a pair of loop-like arms each having a normally lowerand a normally upper end portion and side portions joining said lowerand upper end portions together in a closed loop, said lower endportions being affixed in a spaced parallel relationship with respect toeach other to said beam and said side portions extending angularly apredetermined distance from said surface and intersecting at asubstantial angle of at least about 60* with respect thereto, saidconnecting means includes an elastic belt attached at its ends to saidupper end portions of said loops, and said support means includes aselected portion of a subject''s body, said belt being fastenedthereabout at a predetermined tension and applying a moment to said armsaccording to its instantaneous tension whereby said element is actuatedwith expansion and contrAction of said belt by said body portion toproduce a variable output signal from said element representative of themotions of said body portion.
 3. The invention as defined in claim 2wherein said side portions of said loops extend perpendicularly apredetermined distance from said surface, and said belt includesfastener means adjustable to secure said belt at a tactually establishedpredetermined tension about said body portion.